Wafer processing reactor systems and methods are widely used in the manufacture of semiconductors and integrated circuits. One particular type of wafer processing system utilizes chemical vapor deposition (CVD) to deposit films or layers on the surface of a substrate as a step in the manufacture of semiconductors and integrated circuits. In CVD processes that require multiple gases, the gases are generally combined within a mixing chamber. The gaseous mixture is then coupled through a conduit to a distribution plate or showerhead, which contains a plurality of holes such that the gaseous mixture is evenly distributed into a process region. As the gaseous mixture enters the process region and is infused with energy such as being heated, a chemical reaction occurs between the gases to form a film on a substrate proximate the processing region.
Although it is generally advantageous to mix gases prior to delivery into a process region to ensure that the gases are uniformly distributed into the process region, gases tend to begin reacting within the mixing chamber. Consequently, deposition or etching of the mixing chamber, conduits and other chamber components may occur prior to the gaseous mixture reaching the process region. Additionally, reaction by-products and deposits may accumulate in the chamber gas delivery components.
Some semiconductor processes require delivery of gases into a process region in a sequential manner without premixing. For example, in an atomic layer deposition (ALD) process, which increasingly becomes an alternative to CVD processes, each reactant gas is independently introduced into a reaction chamber through, for example, a showerhead, so that no gas phase intermixing occurs. A monolayer of a first reactant is physi- or chemi-sorbed onto a substrate surface. After the excess first reactant is evacuated from the reaction chamber, a second reactant is then introduced through the showerhead to the reaction chamber and reacts with the first reactant to form a monolayer of the desired film via a self-limiting surface reaction. A desired film thickness is obtained by repeating the deposition cycle as necessary. It is advantageous to introduce the first and second reactants independently and separately through the showerhead to avoid any reaction between the reactants in the showerhead.
Therefore, in either a CVD or an ALD process, it is desired to maintain gases in separate passageways within a showerhead until they exit the showerhead into a process region.
To distribute process gases from a single inlet port to a multitude of outlet holes, gas distribution networks created in a showerhead body may be used. For example, a plurality of parallel channels can be formed in a unitary showerhead body from which a multitude of perpendicular outlet channels deliver process chemicals into a process region. The parallel channels are intersected perpendicularly by a single transverse plenum connected to a central gas source inlet line. Process gas passes from the inlet to the outlets of the showerhead by following a “Cartesian” path by flowing laterally along the transverse plenum, transverse through the parallel channels, and the outlet channels into the process region.
A disadvantage of this design is that there is a large variation in total flow path to reach points of constant radius within the showerhead. As a result, there is typical a large variation in backpressure within the interior flow channels that result in an unacceptable azimuthal and radial variation in outlet gas flow velocity from the multitude of outlet holes. Furthermore, in showerhead designs with a single central gas inlet, there exists an unavoidable time lag between the gases that exist near the center of the showerhead and those existing at the outer perimeter. The large variation in total flow path at points of constant radius inherent with Cartesian-style flow networks creates a “phase error” that may lead to non-uniform chemical concentrations around the perimeter of the showerhead which may affect deposition in transient-flow processes.
To minimize the azimuthal variation in time-lag, radially oriented channels that converge at the center gas inlet may be employed instead of a multitude of parallel channels. However, this type of design leads to a decreasing outlet hole density (hole per square centimeter) due to the divergence of the radial passages. This may be compensated somewhat by additional radial passages at larger radii, however, these require cross-connection to the same source of gas which becomes difficult to do in a truly unit body block of material. Furthermore, it is not apparent that this will yield acceptable flow uniformity either.
Therefore, there is a need of a gas distribution system that provides improved uniform outlet velocity distribution and reduced variation in azimuthal time lag between the gases that exit near the center of the showerhead and those existing at the outer perimeter. Further developments in gas distribution apparatus useful in CVD and ALD processes are needed.